The present invention relates to interconnect sockets for use in holding an integrated circuit (IC) package such as a ball grid array (BGA) package, a chip scale package (CSP) or an IC device of the bare chip type, the sockets being especially suitable for carrying out "burn-in" testing of such IC packages.
Integrated circuit devices each having a plurality of terminals (such as projecting solder balls) arranged in grid-form on its bottom surface are generally known in the art. Usually IC package sockets are used in determining the high frequency characteristics of such IC packages and also in making so-called burn-in tests of such IC packages. One example of such an IC package socket uses a plurality of upright probe pins each containing a spring therein. Another example of an IC package socket uses a plurality of terminals, which are stamped and shaped out of a thin metal sheet. The terminals are so arranged that they may be put in contact with the terminals of the IC package when put in the socket for the purpose of making required electrical connections between the IC package and exterior circuits.
Still another example of an IC package socket, which is proposed as appropriate for use in making a required electrical connection to numerous IC package pins arranged at reduced intervals, comprises an insulating flexible film having a conductive pattern formed thereon, each conductor ending with a metal bump.
As for the IC sockets which use spring-contained pins, each spring must be long enough to assure that a good electrical connection can be made relative to the corresponding one of the terminals of the IC package. In such sockets, the spring-contained pins each are 15 to 20 mm long, and accordingly the inductance of the probe pin is 10 nH or more. Thus, application of signals of several hundred mega-hertz high frequency to an IC package when contained in such an IC package test socket will cause a significant degree of voltage fluctuation due to the relatively large amount of inductance. This will cause an adverse effect on the testing of IC packages in terms of their electrical characteristics, especially in view of a recent tendency to design IC packages to work at a reduced voltage.
Regarding the IC socket which is of the type using stamped terminals, there is a problem of experiencing mismatches between the impedance of the IC package socket and the impedance of the exterior circuit. Such mismatching typically causes reflection of signals and cross-talk between adjacent terminals.
With reference to the type of IC socket which uses flexible circuitry, the conductors of the conductive pattern formed thereon usually extend different distances in radial directions, causing uneven distribution of inductances and impedances in the conductive pattern. Therefore, they often have similar drawbacks as IC package test sockets which incorporate stamped terminals. In testing IC packages, because the conductive projecting balls are arranged in a very close spacing, the testing leads of the test socket must be spread out in order to accommodate the test socket on a printed circuit board. Typically, this is accomplished with the use of a test frame to receive the IC package and, in effect, spread out the leads. Such an approach is expensive, and these frames are large. Avoiding these disadvantageous aspects of testing IC packages having such very close spacing is an important attribute of the invention.